This is based on the OCR A Gateway spec for A level biology, Chapter 23 from module 6. Specification reference: 6.3.1
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Habitat
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Ecological / environmental area inhabited by particular species.
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Population
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Group of organisms of same species in area.
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Community
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Eco. unit composed of different populations.
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Niche
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Role of an organism in an ecosystem (competition occurs when 2 organisms share a niche).
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All affected by biotic + abiotic factors.
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Efficiency at producer level
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Photosynthesis ≠ 100% of sunlight.
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Net production = gross prod. - respiratory losses
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Efficiency at consumer level
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Not all energy consumed (not all eaten or digested, metabolic heat...).
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Ecological efficiency = (energy or biomass available after transfer / energy or biomass available before transfer) x 100
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Detritivors
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Feed on detritus (dead organic material).
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Saprotrophs
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Secrete enzymes in dead material to digest it.
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Recycling nitrogen
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Nitrogen necessary for bio molecules, e.g. nucleic acids, amino acids...
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Nitrogen fixation - Nitrogen cannot be used 'raw', so needs to be bonded with other molecules (by Rhizobium and Azotobacter).
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Nitrification - Ammonium compounds converted into nitrogen-containing compounds.
Requires oxygen. Carried out by Nitrosomonas and Nitrobacter. |
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Denitrification - No oxygen --> denitrifying bacteria convert nitrates into N gas.
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Ammonification - Nitrogen into ammonium compounds.
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Succession
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Type of living organisms changes over time (in plants, from annual plants to hardwood trees).
Communities become increasingly complex, biodiversity increases. |
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Primary succession - Plants colonise barren land for the first time.
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Secondary succession - Soil already present, plants grow for first time.
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Seral stages / seres
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Step in succession.
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Defected succession
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Succession halted before climax community.
If caused by human activity, then = plagioclimax. |
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Pioneer community
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Seeds, spores carried by wind, excrement...
Produce many seeds, germinates quickly, fix N2 from atmosphere. |
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Intermediate community
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Erosion and decomp. of pioneer species form humus. Can support new species (secondary colonisers).
Tertiary colonisers - When conditions improve. Live with little water. |
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Climax community
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Stable, little change over time.
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Distribution
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Where organisms are found in an ecosystem.
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Line or belt transect normally used.
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Abundance
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Number of individuals of a species found in an area.
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Animals - Capture-recapture.
Plants - Individuals per area. |
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D = 1-∑(n/N)2
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D = diversity index
N = total number of organisms in ecosystem n = number of individuals in each species |
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Value between 0-1. Higher value = higher biodiversity.
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